1. Field of Invention
The field of the present invention relates in general to wireless local area networks (WLAN) including wireless access points (WAP) and wireless stations and methods for sounding same.
2. Description of the Related Art
Home and office networks, a.k.a. wireless local area networks (WLAN) are established and serviced using a device called a Wireless Access Point (WAP). The WAP may include a router. The WAP wirelessly couples all the devices of the home network, e.g. wireless stations such as: computers, printers, televisions, digital video (DVD) players, security cameras and smoke detectors to one another and to the Cable or Subscriber Line through which Internet, video, and television is delivered to the home. Most WAPs implement the IEEE 802.11 standard which is a contention based standard for handling communications among multiple competing devices for a shared wireless communication medium on a selected one of a plurality of communication channels. The frequency range of each communication channel is specified in the corresponding one of the IEEE 802.11 protocols being implemented, e.g. “a”, “b”, “g”, “n”, “ac”, “ad”, “ax”. Communications follow a hub and spoke model with a WAP at the hub and the spokes corresponding to the wireless links to each ‘client’ device.
After selection of a single communication channel for the associated home network, access to the shared communication channel relies on a multiple access methodology identified as Collision Sense Multiple Access (CSMA). CSMA is a distributed random access methodology first introduced for home wired networks such as Ethernet for sharing a single communication medium, by having a contending communication link back off and retry access to the line if a collision is detected, i.e. if the wireless medium is in use.
Communications on the single communication medium are identified as “simplex” meaning, one communication stream from a single source node to one or more target nodes at one time, with all remaining nodes capable of “listening” to the subject transmission. To confirm arrival of each communication packet, the target node is required to send back an acknowledgment, a.k.a. “ACK” packet to the source. Absent the receipt of the ACK packet the source will retransmit the unacknowledged data until an acknowledgement is received, or a time-out is reached.
To improve the throughput on each point-to-point link between a WAP and a station, multiple antennas may be used. Multiple-Input Multiple-Output (MIMO) equipped WAPs and stations have been gaining in popularity due to their ability to provide increased performance without the need to increase bandwidth and power. In a MIMO system, both transmitter and receiver have multiple antennas. This creates a matrix channel between the signals coming out of the transmit antennas and the signals observed at the receiver antennas. Where, as in a home or office, the environment has sufficiently rich signal scattering the MIMO system will support simultaneous independent data streams which increases throughput. MIMO transceivers with multiple antennas can exploit any of a number of techniques to increase link throughput specifically: a) controlling how data is loaded on to each antenna, b) how data is coded, and c) how the antennas signals are aimed at the receiving station. Typically, during an association phase the transmitting and receiving device identify their capabilities and agree on a compatible, i.e. common denominator, set of loading, coding and aiming options after which communications are initiated on the link.
In order to characterize the multipath communication channel between the WAP and each station a MIMO sounding is conducted. An explicit sounding as specified in the IEEE 802.11n and 802.11ac standards consists of the transmission of a known sequence from the WAP to each associated station, followed by a sounding response from the station characterizing the communication channel between the WAP and itself. The WAP uses the explicit sounding response to focus its MIMO antennas in a manner which improves either or both signal strength at the station or downlink throughput thereto.
What is needed are improved methods for extending the coverage area between the WAP and its associated stations.